Elevated intra-abdominal pressure leads to major changes in the body's physiology that, if undetected and untreated, can result in organ damage and patient death. When patients become critically ill, they may develop a capillary leak phenomenon that causes the tissues in their body to become edematous with extra fluid that seeps out of the capillaries. This process is called “3rd spacing” of fluid. It is very common in sepsis, burn, trauma and post-operative patients. One area of the body where 3rd spacing is especially prevalent is the abdominal cavity. Critically ill patients can have many liters of fluid leak into the intestinal wall, the intestinal mesentery, and the abdominal cavity (as free fluid sloshing around the intestines).
Fluid 3rd spacing in the abdominal cavity results in an increase in intra-abdominal pressure (IAP). Normal IAP is 0 mm Hg to subatmospheric (less than 0). Once the pressure builds to 12-15 mm Hg, intra-abdominal hypertension (IAH) occurs. At this point, methods to improve intestinal perfusion should be started, such as: fluid loading to increase blood flow to gut, inotropic support to increase cardiac output, etc. As pressures increase above 20-25 mm Hg, the abdominal compartment syndrome (ACS) exists and major physiologic and organ system dysfunction result. Decompressive surgery (vertical midline abdominal incision) is often required to prevent irreversible organ damage and death. The exact pressure at which abdominal decompression should occur is dependent on a number of host factors including age, underlying co-morbidities and physiologic evidence of developing ACS.
Early detection of increasing abdominal pressure allows the clinician to intervene before irreversible organ damage occurs and may be life saving. The only reliable method for early detection of increasing IAP is to place a catheter within a space in the abdomen (peritoneal cavity, stomach, bladder, rectum) and measure the pressure. The most commonly used method is to monitor bladder pressure through an indwelling Foley catheter. To monitor bladder pressure, clinicians are currently building their own devices out of many separate materials and inserting them into the Foley catheter.
Currently employed techniques used to monitor a patient's IAP are adapted to measure the pressure of fluid contained within the patient's bladder at intervals spaced apart in time. While the pressure reading at a pressure transducer may not correspond to the actual value of IAP (e.g. if the transducer is located at a different elevation than the bladder), trends in measured pressure will correlate to trends in IAP in the patient.
One way to measure a patient's IAP involves disassembling a urinary catheter drain tube to inject saline through the catheter and into the patient's bladder. (For convenience, a urinary catheter will generally be referred to in this disclosure as a Foley catheter, due to its common use). Unfortunately, opening the closed drainage system plumbing places both the patient and the health practitioner at increased risk of infection. It is possible to use a three-way Foley catheter, but such catheters are more expensive and are not routinely used. Use of a three-way Foley catheter would require either preknowledge of its necessity, or replacement of a standard catheter. The former option increases costs, and the latter would increase both costs and risk of patient infection.
A different approach for introducing a bolus of fluid into a patient's bladder incorporates the aspiration port included in a urinary catheter drain system as a fluid injection port. The drain tube connected to the Foley catheter is blocked, and the needle of a syringe is passed through the drain tube's aspiration port to permit injection of a saline bolus. A manometer or pressure transducer is then connected to the needle to record bladder pressure. Undesirably, approaches involving use of needles, particularly in the vicinity of the patient's legs to assemble the pressure measuring apparatus, place both the patient and the health practitioner at risk of needle sticks.
With reference to FIG. 1, a currently used arrangement adapted to monitor a medical patient's IAP is generally indicated at 100. A patient is fitted with a urinary catheter 102, such as a Foley catheter. A fluid source, such as saline bag 104, is connected in fluid communication to the catheter 102 upstream of an occluding device 108 temporarily applied to block the catheter drain conduit 106. Interruption of the urine drain path from the patient generally is permitted only temporarily as required to effect pressure measurements.
The device 100 includes a pair of two-way or three-way stopcocks, 110 and 112, respectively. One end of fluid supply tube 114 is connected to a one liter saline bag 104. The other end of fluid supply tube 114 is connected to an inlet port of stopcock 110. A valve stem in stopcock 110 may be oriented to permit fluid to flow from bag 104 toward syringe 116. When syringe 116 is full, or charged with fluid as desired, the valve stem of stopcock 110 is adjusted by way of a manual rotation to permit fluid flow from the syringe toward stopcock 112 while resisting fluid flow toward bag 104. Stopcock 112 can be adjusted to direct a bolus of fluid from syringe 116 for flow through tubing 120 towards catheter 102. Stopcock 112 may also be adjusted to an alternate configuration to provide fluid communication between a pressure measuring device 121 and tubing section 120 while resisting fluid flow toward stopcock 110. An infusion needle or angiocatheter 122 carried at an end of tubing 120 is inserted into urine collection port 125 to couple the tube 120 in fluid communication to the catheter 102.
The steps typically required to measure a patient's IAP, using the arrangement of FIG. 1, are as follows: First the apparatus 100 is assembled, including inserting the needle of an angiocatheter 122 into aspiration port 125 connected to a Foley catheter 102 installed in a patient. Stopcock 110 is oriented to permit fluid flow between bag 104 and syringe 116, and the syringe is filled with saline. Stopcocks 110 and 112 are then both adjusted for fluid flow from the syringe 116 toward the catheter 102. Tube 120 is flushed and filled with saline. Then tubing 106 is occluded to resist fluid flow in a drain direction from catheter 102. Typically, stopcock 112 is then adjusted to resist fluid flow toward syringe 116 and stopcock 110 is configured to permit fluid flow between bag 104 and syringe 116 so that the syringe 116 can be refilled with saline. After priming syringe 116, stopcock 110 and 112 are adjusted for fluid flow between syringe 116 and catheter 102 to place a bolus of fluid into the patient's bladder. Then, stopcock 112 is oriented to provide fluid communication between conduit 120 and pressure transducer 121 while resisting fluid flow toward stopcock 110. Pressure apparatus 121 then indicates the current pressure in the patient's bladder, which may be correlated to IAP. Subsequent to making and recording the pressure measurement, the occlusion of drain 106 is removed to permit draining the bolus of fluid from the patient's bladder. Such procedure is repeated at intervals spaced apart in time to record trends in the patient's IAP. The bolus of injected fluid desirably is less than about 100 mL and of uniform size during each successive pressure measurement to avoid effect from bladder wall musculature on measured pressure.
Occluding device 108 may be a clamp or hemostat as illustrated, or sometimes may be a manually operated valve. However, operable medical grade valves that are commercially available, such as two-way or three-way stopcocks 110 and 112, typically introduce undesired complications. One complication is that the available medical grade stopcocks typically provide drainage passageways that are too small in diameter for use in a urinary catheter drain. Clogging of the urine drain bore would be a serious problem.
The most desirable location of a catheter drain-occluding valve (urine valve) for an IAP measurement system is in close proximity to the catheter 102—therefore between the patient's legs. Another complication substantially precluding direct inclusion of commercially available medical grade two-way or three-way valves or stopcocks is that such devices route fluid conduits in orthogonal directions at the valve connection locations, thereby creating protruding and invasive plumbing that is uncomfortable to the patient. Furthermore, currently available valves and stopcocks also have protrusions (such as valve actuators or handles), and sharp corners or abrupt changes in shape, that place a patient at risk of injury should such protrusion or corner be impressed into a patient's skin.
Because the most desirable plumbing arrangement places the urine valve between a patient's legs, manual actuation of that valve requires a health practitioner to gain physical access to the groin area of a patient. In a surgical setting, the anesthesiologist is the most likely party to assume responsibility for monitoring the patient's IAP. Traditionally, the anesthesiologist is stationed at the patient's head for convenient administration of anesthesia and monitoring of the patient's condition. All monitoring apparatus required by the anesthesiologist desirably is located in close proximity, or in a line-of-sight, to reduce moving about of personnel in the operatory theater.
Historically, in surgeries not involving the head of a patient, the patient's head area is regarded as the “turf” of the anesthesiologist. Correspondingly, the rest of the patient's body is regarded as the “turf” of the surgeon. It is undesirable for the anesthesiologist to move from a traditional station, at the patient's head, repeatedly to make periodic IAP measurements. Further, it would be impolitical to require an anesthesiologist to invade the “turf” of the surgeon to effect the IAP measurement. In any case, periodic manual activation of a urine valve by the anesthesiologist, or other personnel present in the operatory, also may cause an interference with the surgeon.
A variety of valves of various types may be employed in a system to measure IAP. One known plumbing device, typically used to remove a blockage from a drain, may be regarded as a valve, and has a sealing arrangement structured like a balloon disposed inside a pipe. The plumbing device is attached to a hose, and placed through an opening into the blocked drain pipe. Water forced under pressure through the hose inflates the plumbing device to seal the opening into the pipe. Additional water flow through the plumbing device's balloon pressurizes the pipe, hopefully, to flush the blockage downstream through the pipe. Importantly, a fluid path extends from the hose, through the balloon, and into the pipe. The wetted membrane of the aforementioned balloon-in-a-pipe forms a fluid excluding boundary, and creates a 2-dimensional seal interface at a circumference around the inside of the pipe. In correct operation of the plumbing device, fluid never flows between the wetted membrane of its balloon and the interior of the pipe.
A flow-regulating device known as a FLOWGRID valve is described on the world wide web at http://www.mooneycontrols.com/index-products.html. A representative such device is designated a 2″ Large Single Port FLOWGRID valve. Such valves have a pneumatically actuated diaphragm valve element that is biased toward a valve-closed position to restrict fluid flow through the valve. The membrane element is adapted and arranged to occlude the area bounded by the circumference of an entrance orifice, thereby forming a 2-dimensional seal area.
The procedures for measuring trends in a patient's IAP described above undesirably place a patient at risk of infection, or require tiresome manual adjusting of a plurality of plumbing devices, such as two-way valves or stopcocks. It would be a desirable improvement to provide a device for measuring trends in a patient's IAP that is faster and more simple to operate. It would be a further advance to eliminate operations requiring needles to assemble or use the pressure measurement apparatus. A still further advance in the art would enhance the patient's comfort and increase the patient's protection from injury by resisting contact between the patient and uncomfortable or even harmful medical apparatus. A still further advance would provide for actuation of the urine drain valve from a location remote from that valve. It would be an improvement to provide such a valve that is low cost, enhances patient comfort, and/or provides an inherent time-delay in actuation between closed and draining positions. A still further improvement would provide a normally-open valve having a membrane seal arranged for hydraulically-transverse actuation.